Because of limited understanding and the significant clinical relevance of the relationship between pain and motor function in general, and specifically the extent to which oral, face and neck pain affect mandibular function, studies are proposed to employ a randomized, repeated measures cross-over design (before pain, pain, pain control, after pain) to investigate, on an intra-individual level, the effect of experimentally induced and maintained pain on jaw motor function in normal subjects. The applicant will study (1) the mandibular range of motion, (2) the generation of bite force, (3) dental occlusion, (4) mandibular open-close movements, and (5) swallowing, with pain being induced by the infusion of an algesic substance (5% saline) into a) muscles of mastication, b) neck muscles, c) the facial skin, and d) the retromolar mucosa. Infusion of a non-algesic substance (0.9% saline) at a rate equal to the algesic substance will be used as control. Jaw tracking, bite force registration, surface electromyography, motor unit recording, and the assessment of the dental occlusion will be performed to test specific hypotheses about the effect of pain. Electrophysiological experiments in animals have shown that afferent input from different tissues, including nociception, converge even at the first relay. Therefore, it is hypothesized that pain, irrespective of its origin (masticatory muscles, neck muscles, intraoral mucosa, facial skin) causes significant changes in mandibular function. Additional experiments will examine the extent to which masseter pain of increasing intensity and duration affect the mandibular range of motion, and the extent to which range of motion changes following the application of a vapocoolant to the facial skin. These studies address scientifically and clinically important issues, such as whether differences exist between pain originating in the facial skin, masticatory muscles, neck muscles and the oral mucosa as far as the effect on mandibular function is concerned.